For guiding laser beams, it is customary to use either light conductors in the form of flexible glass fibers or transmission systems containing optical deflectors such as mirrors. Particularly for the processing of materials using powerful carbon-dioxide lasers, transmission systems of the above-mentioned type are utilized exclusively because so far no fiber cables are known that provide a sufficiently low-loss transmission in the wavelength range of a carbon-dioxide laser.
The vast majority of known laser machine tools are used for cutting or welding plane workpieces such as sheet metal. In these machines, the laser including its system for beam guidance and focusing is stationary while the workpiece is horizontally moved under the cutting head focusing the laser beam; this movement is in two directions in accordance with the desired contour. A machine of this type is described in U.S. Pat. No. 4,403,134, for example.
On the other hand, devices for laser processing and operating on the basis of conventional machine tools are also known, for example, from German published patent application DE-OS No. 3,226,448, where the cutting head itself is movable in several coordinates. In these devices, the laser generator is installed adjacent to the actual machine tool and its beam is directed along the axes of the machine tool via mirrors coupled to the movable machine parts.
If the laser generator is installed adjacent to the actual machine tool as a separate unit, problems then arise regarding its exact coupling into the beam guidance system of the machine. Relative movements between generator and machine as a result of, for example, vibrations in the foundation, temperature variations, et cetera, can cause an excursion or wandering of the laser beam. Because the position of the focus changes thereby, faulty working results. In the event of larger deviations, the case may even occur that the laser impinges on the mountings of its focusing optics, which, in the case of high-performance lasers having a power of several kilowatts, will inevitably destroy them.
In laser systems for reading out the contents of information storage plates, it is known to provide control arrangements which guide the focus of the laser beam radially along a predetermined track. In this connection, reference may be had to German Pat. No. 26 30 381. However, the control arrangements for such low-power laser systems evaluate the deviation of the focus from the visibly marked data track. Control arrangements operating on this basis are of no use for laser manufacturing processes. In these processes, it is sufficient to correct deviations of the focus position by a recalibration between the working steps as is described in German published patent application DE-OS No. 31 34 556.